In the ongoing war against cancer, an international team led by scientists from Johns Hopkins University, US, have for the first time found what causes the spread of cancer, and what could slow it down.

This is important because 90% of cancer deaths are caused when cancer cells break off from the origin and start spreading elsewhere in the body. There are no existing drugs for stopping this spread, known as metastasis, of cancer.

The researchers found that when cancer cells get densely packed they secrete two proteins that deliver a stark message to other cells: go away.

This causes the cancer cells to break off from the pack and float through the blood stream or lymphatic system to other sites and start growing afresh.

"It's like waiting for a table in a severely overcrowded restaurant and then getting a message that says you need to take your appetite elsewhere," said lead author Hasini Jayatilaka who hails from Sri Lanka. The study is published in Nature Communications.

"We found that it was not the overall size of a primary tumor that caused cancer cells to spread, but how tightly those cells are jammed together when they break away from the tumor."

Jayatilaka and her colleagues found a medication mix that kept this microscopic message from being delivered.

The team members cautioned that this treatment was tested in animal models, but not yet on human cancer patients. Nevertheless, they said the discovery contributes to a promising new focus for cancer research: disrupting the biochemical activity that prods cancer cells to spread through the body. One of the study's senior authors, Denis Wirtz, also from Johns Hopkins and director of its Physical Sciences-Oncology Center, said no commercial drugs are now being produced specifically to inhibit metastasis because drug companies believe the best way to stop cancer from spreading is to destroy the primary tumor from which it originates.

"The pharmaceutical companies view metastasis as a by-product of tumor growth," said Wirtz. "Our study looked more closely at the steps that actually initiate metastasis. This treatment has the potential to inhibit metastasis and thus improve cancer patient outcomes."

The team found that two existing drugs -Tocilizumab and Reparaxin-prevented cancer cells from getting their marching orders. Tocilizumab is an approved medication for rheumatoid arthritis and is in trials for use in ovarian cancer cases. Reparaxin is being evaluated as a possible treatment for breast cancer.

"In our eight-week experiment, when we used these two drugs together, the growth of the primary tumor itself was not stopped, but the spread of the cancer cells was significantly decreased," Jayatilaka said. "We discovered a new signaling pathway that, when blocked, could potentially curb cancer's ability to metastasize."